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authorThomas Gleixner <tglx@linutronix.de>2008-10-17 10:01:23 +0200
committerThomas Gleixner <tglx@apollo.(none)>2008-10-17 18:13:38 +0200
commitfb02fbc14d17837b4b7b02dbb36142c16a7bf208 (patch)
tree9df1d069c5612047c38a9f6d6dc801ee0369ae3c
parentc34bec5a44e9486597d78e7a686b2f9088a0564c (diff)
downloadop-kernel-dev-fb02fbc14d17837b4b7b02dbb36142c16a7bf208.zip
op-kernel-dev-fb02fbc14d17837b4b7b02dbb36142c16a7bf208.tar.gz
NOHZ: restart tick device from irq_enter()
We did not restart the tick device from irq_enter() to avoid double reprogramming and extra events in the return immediate to idle case. But long lasting softirqs can lead to a situation where jiffies become stale: idle() tick stopped (reprogrammed to next pending timer) halt() interrupt jiffies updated from irq_enter() interrupt handler softirq function 1 runs 20ms softirq function 2 arms a 10ms timer with a stale jiffies value jiffies updated from irq_exit() timer wheel has now an already expired timer (the one added in function 2) timer fires and timer softirq runs This was discovered when debugging a timer problem which happend only when the ath5k driver is active. The debugging proved that there is a softirq function running for more than 20ms, which is a bug by itself. To solve this we restart the tick timer right from irq_enter(), but do not go through the other functions which are necessary to return from idle when need_resched() is set. Reported-by: Elias Oltmanns <eo@nebensachen.de> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Tested-by: Elias Oltmanns <eo@nebensachen.de>
-rw-r--r--kernel/time/tick-broadcast.c13
-rw-r--r--kernel/time/tick-internal.h2
-rw-r--r--kernel/time/tick-sched.c31
3 files changed, 38 insertions, 8 deletions
diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index cb01cd8..f98a1b7 100644
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -384,6 +384,19 @@ int tick_resume_broadcast_oneshot(struct clock_event_device *bc)
}
/*
+ * Called from irq_enter() when idle was interrupted to reenable the
+ * per cpu device.
+ */
+void tick_check_oneshot_broadcast(int cpu)
+{
+ if (cpu_isset(cpu, tick_broadcast_oneshot_mask)) {
+ struct tick_device *td = &per_cpu(tick_cpu_device, cpu);
+
+ clockevents_set_mode(td->evtdev, CLOCK_EVT_MODE_ONESHOT);
+ }
+}
+
+/*
* Handle oneshot mode broadcasting
*/
static void tick_handle_oneshot_broadcast(struct clock_event_device *dev)
diff --git a/kernel/time/tick-internal.h b/kernel/time/tick-internal.h
index 4692487..b1c05bf 100644
--- a/kernel/time/tick-internal.h
+++ b/kernel/time/tick-internal.h
@@ -36,6 +36,7 @@ extern void tick_broadcast_switch_to_oneshot(void);
extern void tick_shutdown_broadcast_oneshot(unsigned int *cpup);
extern int tick_resume_broadcast_oneshot(struct clock_event_device *bc);
extern int tick_broadcast_oneshot_active(void);
+extern void tick_check_oneshot_broadcast(int cpu);
# else /* BROADCAST */
static inline void tick_broadcast_setup_oneshot(struct clock_event_device *bc)
{
@@ -45,6 +46,7 @@ static inline void tick_broadcast_oneshot_control(unsigned long reason) { }
static inline void tick_broadcast_switch_to_oneshot(void) { }
static inline void tick_shutdown_broadcast_oneshot(unsigned int *cpup) { }
static inline int tick_broadcast_oneshot_active(void) { return 0; }
+static inline void tick_check_oneshot_broadcast(int cpu) { }
# endif /* !BROADCAST */
#else /* !ONESHOT */
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 7aedf43..0581c11 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -508,10 +508,6 @@ static void tick_nohz_handler(struct clock_event_device *dev)
update_process_times(user_mode(regs));
profile_tick(CPU_PROFILING);
- /* Do not restart, when we are in the idle loop */
- if (ts->tick_stopped)
- return;
-
while (tick_nohz_reprogram(ts, now)) {
now = ktime_get();
tick_do_update_jiffies64(now);
@@ -557,6 +553,27 @@ static void tick_nohz_switch_to_nohz(void)
smp_processor_id());
}
+/*
+ * When NOHZ is enabled and the tick is stopped, we need to kick the
+ * tick timer from irq_enter() so that the jiffies update is kept
+ * alive during long running softirqs. That's ugly as hell, but
+ * correctness is key even if we need to fix the offending softirq in
+ * the first place.
+ *
+ * Note, this is different to tick_nohz_restart. We just kick the
+ * timer and do not touch the other magic bits which need to be done
+ * when idle is left.
+ */
+static void tick_nohz_kick_tick(int cpu)
+{
+ struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+
+ if (!ts->tick_stopped)
+ return;
+
+ tick_nohz_restart(ts, ktime_get());
+}
+
#else
static inline void tick_nohz_switch_to_nohz(void) { }
@@ -568,9 +585,11 @@ static inline void tick_nohz_switch_to_nohz(void) { }
*/
void tick_check_idle(int cpu)
{
+ tick_check_oneshot_broadcast(cpu);
#ifdef CONFIG_NO_HZ
tick_nohz_stop_idle(cpu);
tick_nohz_update_jiffies();
+ tick_nohz_kick_tick(cpu);
#endif
}
@@ -627,10 +646,6 @@ static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
profile_tick(CPU_PROFILING);
}
- /* Do not restart, when we are in the idle loop */
- if (ts->tick_stopped)
- return HRTIMER_NORESTART;
-
hrtimer_forward(timer, now, tick_period);
return HRTIMER_RESTART;
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